A spacecraft designed to gather samples of dust spewed from a comet and return the dust to Earth for detailed analysis has been selected to become the fourth flight mission in NASA's Discovery program.

Known as Stardust, the mission also will gather and return samples of interstellar dust that the spacecraft encounters during its trip through the Solar System to fly by a comet called Wild-2 in January 2004. Stardust was one of three Discovery mission proposals selected for further study as part of a February 1995 announcement by NASA that a Moon-orbiting mission called Lunar Prospector had been selected as the third Discovery flight.

"Stardust was rated highest in terms of scientific content and, when combined with its low cost and high probability of success, this translates into the best return on investment for the nation," said Dr. Wesley T. Huntress Jr., NASA Associate Administrator for Space Science. "The Stardust team also did an excellent job of updating their plan to communicate the purpose and results of this exciting mission to educators and the public."

The Stardust mission team is led by Principal Investigator Dr. Donald Brownlee of the University of Washington in Seattle, with Lockheed-Martin Astronautics, Denver, as the contractor building the spacecraft. NASA's Jet Propulsion Laboratory will provide project management.

Comet Wild-2 is known as a "fresh comet" because its orbit was deflected from much farther out in the Solar System by the gravitational attraction of Jupiter in 1974. Stardust will approach as close as 100 kilometers (62 miles) to the comet's nucleus.

"Space scientists are intensely interested in comets because we believe that most of them are well-preserved remnants from the earliest days of star and planetary formation," Huntress said. "Stardust should also give us some unique guidance about how to focus the science we plan to conduct a few years later with a surface lander on a different comet during the international Rosetta mission."

Stardust will be launched on an expendable launch vehicle in February 1999 for a total mission cost to NASA in real-year dollars of $199.6 million. The return capsule carrying the dust samples would parachute to Earth in a landing on a dry Utah lake bed in January 2006.

Stardust will use an unusual material called aerogel to capture the dust samples. This porous, extremely low density material is somewhat like glass in that it is made of silica -- a pure form of sand -- and it has about the same melting point. Although aerogel does not absorb moisture, the strangely fluorescent substance can absorb large amounts of gas or particle matter due to its remarkable internal surface area.

The spacecraft will also carry an optical camera that should return cometary images with 10 times the clarity of those taken of Halley's Comet by previous space missions, as well as a mass spectrometer provided by Germany to perform basic compositional analysis of the samples while in-flight.

Stardust was selected over a proposed mission to study the circulation of the atmosphere of Venus, known as the Venus Multiprobe, and a proposed mission to collect samples of particle matter from the Sun, called Suess-Urey. These three missions and Lunar Prospector were among 28 Discovery proposals submitted to NASA in October 1994 in response to an August 1994 announcement of opportunity.

The first two missions in the Discovery program will be launched in 1996, in February and December, respectively: the Near Earth Asteroid Rendezvous, a small spacecraft that will orbit and study the asteroid Eros beginning in January 1999; and the Mars Pathfinder, designed to place a small lander and robotic rover on the surface of Mars in July 1997.

Formally started in NASA's FY 1994 budget, the Discovery program features small planetary exploration spacecraft with focused science goals that can be built in 36 months or less, for less than $150 million (FY '92 dollars), not including the cost of the launch vehicle. The program grew out of a series of discussions and workshops that NASA has held with the space science community.